The amine borane compound such as trihydro(N-methylmethanamine)boron represented by the formula (CH.sub.3).sub.2 NH:BH.sub.3 or (N,N-dimethylmethanamine)trihydroboron represented by the formula (CH.sub.3).sub.3 N:BH.sub.3 finds a wide variety of uses as an industrial reagent. For example, the amine borane compound is used as a reducing agent in the plating, photographic development and production of printed circuit boards.
The above amine borane compound is commonly produced by reacting an amine salt with sodium borohydride of the formula NaBH.sub.4. However, the purity of the amine borane compound obtained by this reaction is not always high, so that, after the completion of the reaction, the amine borane compound must be purified by, for example, recrystallization.
For example, Japanese Patent Laid-open Publication No. 56(1981)-158792 discloses a process comprising reacting an amine salt with sodium borohydride in dimethoxyethane as a reaction solvent, distilling off dimethoxyethane as the reaction solvent from the obtained reaction mixture, dissolving the resultant distillation residue in an organic solvent such as benzene or dichloromethane, removing impurities by filtration and distilling off the solvent to thereby obtain a purified amine borane compound. However, in this process, a large amount of organic solvent such as benzene or dichloromethane is used in the purification with the result that high cost is incured and a problem of work environment is encountered. Furthermore, the yield and purity of the amine borane compound are not necessarily satisfactory, thereby leaving room for improvement.
Japanese Patent Laid-open Publication No. 10(1998)109991 discloses a process in which the purification after the reaction comprises distilling off 1,2-dimethoxyethane as a reaction solvent from the obtained reaction mixture, adding water and a water insoluble organic extractant or the mixture thereof so that an organic phase and a water phase are formed, separating the organic phase from the water phase and distilling the organic phase to thereby obtain an amine borane compound. The organic extractant used in the process is an aromatic hydrocarbon, a halogenated hydrocarbon or the like, so that, as in the process of Japanese Patent Laid-open Publication No. 56(1981)-158792, room for improvement is left in terms of cost, work environment, product yield and product purity.
The present invention has been made in view of the above prior art. The object of the present invention is to provide a process for producing an amine borane compound, wherein the amine borane compound formed by the reaction of an amine salt and sodium borohydride can be purified to a high degree with low cost, safely and at a high yield.